Method and apparatus for controlling the temperature of blast furnace gases



Jan. 17, 1967 l.. F. GRACE ETAL. 3,298,824

METHOD AND APPARATUS FOR CONTROLLING THE TEMPERATURE OF BLAST FURNACE GASES Filed Nov. 22, 1965 Aller/rey United States Patent O 3,298,824 METHOD AND APPARATUS FR CONTROLLING THE TEMPERATURE F BLAST FURNACE GASES Lloyd Francis Grace, Franklin Township, Westmoreland,

Pa., and William Patrick Manning, Tulsa, Okla., assignors to United States Steel Corporation, a corporation of Delaware Filed Nov. 22, 1965, Ser. No. 509,073 8 Claims. (Cl. 75-41) This invention relates to a method and apparatus for controlling the temperature of blast furnace gases, and more particularly to controlling the temperature of the gases at the top of the blast furnace stack. If the temperature is too high, warping of the furnace structural parts, such as off-takes and t-he bottom bell, results. If the temperature is too low, condensation occurs on the interior structural walls. The top gas temperatures are ordinarily maintained between 250 and 600 F. A certain amount of temperature fluctuation due to charging of the furnace is unavoidable. Cooling of the top gas has been accomplished by spraying water or injecting low pressure steam into the top of the blast furnace, but no simple way of raising top gas temperature is available. As a result, a relatively high temperature has been maintained to avoid excessive low gas temperatures with their resulting condensation. High temperature, of course, causes heat loss.

It is, therefore, an object of our invention to provideV apparatus for maintaining the temperature of the top gases within a relatively narrow `range so as to permit more efficient operation.

, 3,298,824 Patented Jan.A 17, 1967 A heating device may be provided for the gases in duct 8 below the connection 12 and a cooling device 22 may be provided for the gases in duct 8 above the connection 12. A temperature measuring device, such as a thermocouple 24, is provided in the off-take 6 to measure the temperature of the gases above the stockline S. The thermocouple 24 is connected to temperature control devices 16T and 18T. These controls may be any standard type such as Honeywell Electronik Pneumatic Controllers Type Air-O-Line as shown on page 38 of catalogue No. C15-2A (copyright 1960).

During normal operation, when the temperature of the gases above the stockline S is between a preset limit, valves 16 and 18 will be closed. When the temperature of the gases determined by thermocouple 24 is above the preset maximum, temperature controller 18T will operate to open valve 18 through actuator 18A. When this occurs, the burden in the stack 2 will absorb more of the sensible heat in the remaining gases and thus lower the temperature of the gases more than when all of the gases are passing through the burden. If desired,l the controller 16T can be set to open valve 16 so as to obtain a more pronounced cooling effect at the stockline. However, this will not ordinarily be done. If the temperature of the gases in the off-take 6 outside of the furnace becomes too high the cooling device 22 can be used to cool the by-passed gases.

When the temperature of the gases above the stockline S, as determined by thermocouple 24, falls below a preset level the temperature control 16T will cause the valve 16 to open. At this time valve 18 will be closed since it is only open when the temperature is too high. This Another object is to provide a method of controlling pressure steam into the top of the blast furnace stack.

A still further object is to provide such a method which will lower the coke rate.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which:

FIGURE 1 is a schematic view, partly in section, showing one embodiment of our invention; and

FIGURE 2 is a view, similar to FIGURE 1, showing a second embodiment of our invention.

Referring more particularly to the drawings, reference numeral 2 indicates a blast furnace stack having the usual burden B therein which extends to the stockline S. A large bell 4 and off-takes 6 are provided `at the top of the furnace in the usual manner. According to our invention we provide a duct 8 which extends from a substantial distance lbelow the stockline to Voff-take 6. While it is preferred that a duct 8 be associated with each ott-take 6, only one will be described in detail since they all will be constructed in the same manner. An entry grate 10 at the bottom connection of the duct 8 to the stack 2 permits passage of gases from the stack to the duct while preventing the burden materials Isuch as coke, iron ore and limestone from passing out into the duct. A branch duct 12 connects the duct 8 to the stack 2 a short distance below the stockline S. A grate 14 at the furnace end of duct 12 serves the same purpose as grate 10. A valve 16 is positioned in the duct 8 below the connection 12 and asimilar valve 18 is positioned in the duct 8 above the connection 12. The valves 16 and 18 are preferably air operated butterfly valves such yas shown on .page 42 of Honeywell catalogue No. C800-1 (copyright 1958). The valves 16 and 18 are preferably equipped with actuators 16A and 18A such as Honeywell Series 800 Actuators as shown on page 45 of catalogue No. C800-1.

lonly periodic heating is required.

causes a portion of the gases to short circuit the part of the blast furnace stack between grates 10 and 14. The short circuited gases will have a higher temperature than normal since the sensible heat tlierein is not taken away by the burden and there will be an increase in the temperature of the combined stack'gases above the stockline. The heating effect can be increased by means of the heating chamber 20. The heating may be obtained either by burning the gases themselves or by lthe use of external Iheat. For efficient operation insulation 26 is provided laround the duct 8.

In some operating conditions with certain burdens experience has shown that the top gas temperature will not be too low and it is only necessary to prevent the temperature from getting too high. With the furn-ace operating under these conditions at all times the branch duct 12 and one of the valves 16 and 18 can be omitted and cooling will 'be accomplished in the same manner as described before.

FIGURE 2. shows an arrangement of apparatus where In this embodiment, a duct 30 is provided which corresponds to that portion of the duct 8 between grating 10 and 14. A valve 32 similar to valve 16 is provided in the duct 30 and is provided with an actuator 32A which is connected to a pressure switch 34, which in turn is connected to a temperature controller 32T similar to temperature controller 16T. Thermocouple 24 is connected to temperature controller 32T. A combustion chamber 36 is provided in the duct 30. Air is provided for the combustion chamber 36 from a blower 38 through duct 40 having a valve 42 therein. The combustion chamber 36 may be a l5 in. inside diameter refractory lined chamber 2 ft. long. The blower 38 may be a standard blower such as a Rotron Model A Blower, type B.S.-702 as shown on Rotron Manufacturing Company, Inc., catalogue sheet 40l0l-10B having a capacity of 800 standard cu. ft. per minute. Valve 42 may be a Honeywell 8 in. butterfly valve as shown in catalogue No. C800-1 operated by actuator 42A. Blower 3 motor 38M is supplied with power from a 440-volt power source L1, L2 through a pneumatic relay 44 which is actuated from pressure switch 34. A pilot 46 of any standard type is provided for igniting the gases in the chamber 36.

In operation, when the temperature of the gases above the stockline S fall below a preset temperature, the temperature control 32T will operate the pressure switch 34 to open valve 32 and close relay 44 so as to start the motor 38M in operation. The gases flowing into chamber 36 will be ignited and returned to the stack 2 through grating 14, thus increasing the `temperature of the gases a-bove the stockline S. If desired, -a thermocouple 4S may be provided in the combustion chamber 36 and connected to a temperature control 42T which is operable to close valve 42 when the temperature reaches a predetermined maximum.

When the temperature of the removed gases is raised, either by outside source or by burning the gases, it is necessary that they be returned to the furnace a sufficient distance below the stockline S to permit mixing of the hot gases with the stack gases passing through the burden in the usual manner. Experiments indicate that this distance should be at least 2 ft. In one experimental blast furnace, 5% of the blast furnace gases were withdrawn periodically from the stack at a point 8 ft. below the stockline with part of the gases being burned to raise the final temperature of the withdrawn gases to 2500 F. These gases were then returned to the blast furnace gas 2 ft. below the stockline. The range in blast furnace top gas temperature with this arrangement was between 200 and 275 a-s compared to a range of between 200 and over 400 without the withdrawal of the gases.

While several embodiments of `our invention have been shown and described it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

We claim:

1. In a blast furnace including a stack having a burden therein extending upwardly to a stockline below the top of the 4stack and through which combustible blast furnace gases lpass upwardly; apparatus for controlling the temperature of the blast furnace ,gases at the top of the blast furnace stack comprising a duct, a connection between the lower end `of said duct :and the burden containing portion of the stack at `an elevation a substantial distance below the stockline, a second connection between said duct and said stack at an elevation above said rst connection and below said stockline, a valve in said duct be-tween said connections for controlling flow of gases through said duct, and means for opening said valve when the temperature of the combustible gases at the top of the stack fall below a predetermined level.

2. Apparatus according to claim 1 including means for 3. Apparatus according to claim 1 including a third connection between said duct and the blast furnace above said stockline, a valve in said duct between said second and third connection-s for controlling flow of gases through said duct, and means for opening said last named valve when the temperature of the combustible gases at the top of the stack rise above a predetermined level.

4. Apparatus according to claim 3 including means for burning the blast furnace gases in said duct between the first and second connections when the temperature of the blast furnace gases at the top of the blast furnace stack fall below a predetermined level.

5. Apparatus laccording to claim 4 including means forv cooling the gases in said duct between said second and third connections.

6. Apparatus according to claim 3 including means for automatically opening said first named valve and closing said second named valve when the temperature of the blast furnace gases at the top of the blast furnace stack fall below a predetermined level, said last named means closing said first named valve and opening said second named valve when the temperature of the blast furnace gases at the top of the blast furnace stack rise above 4a predetermined level.

burning the blast furnace gases in said duct when the temperature of the blast furnace gases at the top of the blast furnace stack fall below a predetermined level.

7. The method of operating a blast furnace of the type including a stack having a burden therein extending upwardly to a stockline below the top of the stack and through which combustible blast furnace gases pass upwardly; which method comprises removing a portion of the blast furnace gases from the burden containing portion of the stack a substantial distance below the stockline when the temperature of theblast furnace gases above the stockline is below a predetermined level, and mixing the removed gases with the remaining blast furnace gases at a higher elevation below the stockline.

8. The method of claim 7 in which the gases are removed a short distance below the stockline and :are mixed with the remaining gases above the stockline when the temperature of the blast furnace gases at the top of the blast furnace stack rise above a predetermined level.

References Cited by the Examiner UNITED STATES PATENTS 409,541 8/ 1889 Williams 266-14 620,339 2/ 1899 Machell 266--31 676,692 6/ 1901 Hartman 266-31 1,649,201 11/1927 Vanderstein 266-14 1,694,376 12/1928 Day et al. 266-14 1,740,886 12/l929 Barr et al. 266-31 2,283,163 5/tl942 Brassert et al. 266-35 2,549,720 4/ 1951 Strassburger 266-31 2,697,598 12/1954 Afeck 266-32 JOHN F. CAMPBELL, Primary Examiner.

L. I. WESTFALL, Assistant Examiner. 

1. IN A BLAST FURNACE INCLUDING A STACK HAVING ABURDEN THEREIN EXTENDING UPWARDLY TO A STOCKLINE BELOW THE TOP OF THE STACK AND THROUGH WHICH COMBUSTIBLE BLAST FURNACE GASES PASS UPWARDLY; APPARATUS FOR CONTROLLING THE TEMPERATURE OF THE BLAST FURNACE GASES AT THE TOP OF THE BLAST FURNACE STACK COMPRISING A DUCT, A CONNECTION BETWEEN THE LOWER END OF SAID DUCT AND THE BURDEN CONTAINING PORTION OF THE STACK AT AN ELEVATION A SUBSTANTIAL DISTANCE BELOW THE STOCKLINE, A SECOND CONNECTION BETWEEN SAID DUCT AND SAID STACK AT AN ELEVATION ABOVE SAID FIRST CONNECTION AND BELOW SAID STOCKLINE, A VALVE IN SAID DUCT BETWEEN SAID CONNECTIONS FOR CONTROLLING FLOW OF GASES THROUGH SAID DUCT, AND MEANS FOR OPENING SAID VALVE WHEN THE TEMPERATURE OF THE COMBUSTIBLE GASES AT THE TOP OF THE STACK FALL BELOW A PREDETERMINED LEVEL.
 7. THE METHOD OF OPERATING A BLAST FURNACE OF THE TYPE INCLUDING A STACK HAVING A BURDEN THEREIN EXTENDING UPWARDLY TO A STOCKLINE BELOW THE TOP OF THE STACK AND THROUGH WHICH COMBUSTIBLE BLAST FURNACE GASES PASS UPWARDLY; WHICH METHOD COMPRISES REMOVING A PORTION OF THE BLAST FURNACE GASES FROM THE BURDEN CONTAINING PORTION OF THE STACK OF SUBSTANTIAL DISTANCE BELOW THE STOCKLINE WHEN THE TEMPERATURE OF THE BLAST FURNACE GASES ABOVE THE STOCKLINE IS BELOW A PREDETERMINED LEVEL, AND MIXING THE REMOVED GASES WITH THE REMAINING BLAST FURNACE GASES AT A HIGHER ELEVATION BELOW THE STOCKLINE. 